IARC classifications

From National Cancer Control Policy

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IARC classifications


The International Agency for Research on Cancer (IARC) have devised a system of categories to evaluate the carcinogenicity of an agent to humans[1]. An agent is classified based on scientific evidence derived from human and experimental animal studies and from mechanistic and other relevant data[2]. The list of categories and their definition are shown in Table 1.

Table 1. IARC classifications of carcinogenic agents[1][2]

Group Description Definition Number of agents
Group 1 Carcinogenic to humans
  • Sufficient evidence of carcinogenicity OR
  • Evidence of carcinogenicity in humans is less than sufficient but there is sufficient evidence of carcinogenicity in experimental animals and strong evidence in exposed humans that the agent acts through a relevant mechanism of carcinogenicity
111
Group 2A Probably carcinogenic to humans*
  • Limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals OR
  • Inadequate evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals and strong evidence that the carcinogenesis is mediated by a mechanism that also operates in humans OR
  • Limited evidence of carcinogenicity in humans, but belongs, based on mechanistic considerations, to a class of agents for which one or more members have been classified in Group 1 or Group 2A
66
Group 2B Possibly carcinogenic to humans*
  • Limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals OR
  • Inadequate evidence of carcinogenicity in humans but sufficient evidence of carcinogenicity in experimental animals OR
  • Inadequate evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals, but with supporting evidence from mechanistic and other relevant data
285
Group 3 Not classifiable as to its carcinogenicity to humans
  • Evidence of carcinogenicity is inadequate in humans and inadequate or limited in experimental animals OR
  • Evidence of carcinogenicity is inadequate in humans but sufficient in experimental animals, but strong evidence that the mechanism of carcinogenicity in experimental animals does not operate in humans OR
  • Agents that do not fall into any other group


Agents in Group 3 are not determined to be non-carcinogenic or safe overall, but often means that further research is needed.

505
Group 4 Probably not carcinogenic to humans
  • Evidence suggesting lack of carcinogenicity in humans and in experimental animals OR
  • Inadequate evidence of carcinogenicity in humans but evidence suggesting lack of carcinogenicity in experimental animals, consistently and strongly supported by a broad range of mechanistic and other relevant data
1

* The terms probably carcinogenic and possibly carcinogenic have no quantitative significance and are used simply as descriptors of different levels of evidence of human carcinogenicity, with probably carcinogenic signifying a higher level of evidence than possibly carcinogenic.

References

  1. 1.0 1.1 International Agency for Research on Cancer. Agents classified by the IARC monographs, volumes 1–108. [homepage on the internet] Lyon: IARC; 2017 Nov 23 [cited 2013 Oct 21; updated 2013 Jul 16]. Available from: http://monographs.iarc.fr/ENG/Classification/index.php.
  2. 2.0 2.1 International Agency for Research on Cancer. Preamble to the IARC monographs - scientific review and evaluation. [homepage on the internet] Lyon: IARC; 2006 Jan 23 [cited 2013 Oct 21; updated 2013 Oct 21]. Available from: http://monographs.iarc.fr/ENG/Preamble/currentb6evalrationale0706.php.

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